A semiconductor processing assembly may typically comprise a substrate cassette exchange station for exchanging substrate cassettes with a fab substrate cassette transport system, such as an Over Head Transport system. In this respect, it is desirable that a semiconductor processing assembly comprises a substrate cassette stocker for stocking one or more cassettes. This provides greater flexibility in a cassette logistics.
For instance, in a semiconductor processing assembly including a batch semiconductor processing system, wherein a batch comprises wafers from a plurality of substrate cassettes, it is convenient if all substrate cassettes involved can be stored at the system. After loading the batch of wafers from the substrate cassettes into the semiconductor processing system, the empty substrate cassettes can then stay with the system during processing. After completion of the treatment, the cassettes may readily be filled with processed wafers, without a need to transport the cassettes in the intermediate time.
Typically, a substrate cassette stocker is positioned at the front of a semiconductor processing assembly, in a clean room bay area of the processing facility. With growing wafer size, and in particular with 450 mm wafer size, such front-side substrate cassette stockers require a lot of precious space. This is because they need not only provide for space for the stocker positions/substrate cassette accommodations, but also for maneuvering of the substrate cassettes.
Efficient use of clean room floor space is important in semiconductor processing facilities. Typically a processing system is disposed in a clean room chase area or service area, with a front face flush with a bounding wall of a clean room bay area. The processing system may include a substrate cassette exchange station, arranged at the front of the processing system, and configured to receive substrate cassettes, containing substrates to be processed, from the clean room bay area.
In addition to a small foot print in the chase area, a small face print with the clean room bay area wall is desirable. Typically the chase area and the bay area have similar clean room classifications. Often, in the chase area space is available that cannot be utilized because no clean room wall is available to place additional systems. Generally, the length or depth of a processing system, i.e. the dimension of the processing system perpendicular to the clean room wall, may vary between different systems and the chase area may be dimensioned to accommodate processing systems with a certain maximum depth. When only systems with a smaller depth, e.g. a small or medium depth, are used, a significant part of the chase area is necessarily left unused.
EP 1 146 451 A2 discloses a fabrication system and a method of promoting fault tolerant production capacity for semi-conductor processing equipment. The fabrication system includes a transport aisle or bay area that is bounded by a clean room wall and a clean room or chase area in which a plurality of semiconductor processing tools are positioned. Additionally, within the clean room a storage apparatus is accommodated that extend perpendicular to the transport aisle and that has one or more load ports adapted to receive a wafer carrier from a factory transport agent (e.g., an overhead conveyor, an automatic guided vehicle, FAB personnel, etc.). Each processing tool has one or mor tool loading platforms coupled thereto, such that one or more wafer carriers may be transferred from the tool loading platform to the respective processing tool. The storage apparatus is a separate unit from the processing tools and may comprise a vertical transfer mechanism (such as an elevator or pick and place robot) and a horizontal transfer mechanism (such as a conveyor or a shelf coupled to a pick and place robot). The storage apparatus may comprise a conveyor adapted to transfer a wafer carrier between processing tools within the clean room.